Boiler Short Cycles After Draining & Refilling

Drained my boiler to flush it, then refilled. When the boiler was turned back on it would cycle on for about 10-15 seconds then cut off and the module would flash 'Recycle', minute later kick back on for another 10 seconds give or take. did this a few times, then i felt the circulator kick in on one of the recycles.....the boiler stopped recycling after a few times and now operates normal.

What would cause this after a refill?

Also my guage crapped out on me so I picked up one at home depot, got all the way back just to find out i need a 1/2 NPT not a 1/4....seems like all home depot had was 1/4"....are 1/4 more common?

Boiler is a Well Mclain Gold.

air pressure could be building up from the drain, shutting off the boiler until the bleeders get it purged and pressure returns to normal.
1/4" pipe thread is pretty much standard for gauges, your old one may have an adapter on it to bump it up to 1/2"
most boilers have a temp/pressure combo gauge that fits in a 1/2" pipe plug.

You need to get the right gauge. A hot water heating company will have this. Air in the system will cause the problem you had. Try to vent the system as it is being refilled. You might call a service man the next time. We do not drain a hot water system unless we have to.

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Originally Posted by greenhorn0311

Drained my boiler to flush it, then refilled. When the boiler was turned back on it would cycle on for about 10-15 seconds then cut off and the module would flash 'Recycle', minute later kick back on for another 10 seconds give or take. did this a few times, then i felt the circulator kick in on one of the recycles.....the boiler stopped recycling after a few times and now operates normal.

What would cause this after a refill?

Also my guage crapped out on me so I picked up one at home depot, got all the way back just to find out i need a 1/2 NPT not a 1/4....seems like all home depot had was 1/4"....are 1/4 more common?

Boiler is a Well Mclain Gold.

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what was the reason for flushing the system? was it reccomended? was the pump running the entire time the burner was recycling?

So you have a sealed system that cannot introduce new mineral content and you flushed the system which will probably not remove any buildup so you can add more mineral laden water to the system?

Residential hydronic heating systems most often have tap water as the heat transfer medium. As suggested, this is usually hard water. The salts "hardness" of this tap water will precipitate (come out) of solution with the high temperatures of a typical boiler driven heating system. The deposits will usually form at the heat transfer surface and degrade heat transfer at the source (worst place possible). This layer of salts (magnesium and calcium) will create an insulative layer between burner and water costing the owner more in fuel consumption. This is usually a permanent condition unless the system is drained or "flushed" again, in which case the layer of salts is increased and heat transfer efficiency further degraded.

Furthermore, any fresh tap water introduced to a closed hydronic heating system introduces fresh oxygen in solution. This oxygen will attach all ferrous components in the system and deposit iron oxides throughout and have the added effect of degrading pump performance.

This is why good hydronic heating designs include isolation of near piping (where the majority of serviceable components should be placed) from distribution piping and terminals (radiators, radiant floors, fan coils) so that the majority of the system need never be drained.

We test, clean and treat hydronic heating systems but it all starts with a proper test.

DIY boilers service. Always the first mistake.

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Originally Posted by kangaroogod

So you have a sealed system that cannot introduce new mineral content and you flushed the system which will probably not remove any buildup so you can add more mineral laden water to the system?

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maybe it was plugged? i wish he would tell us why he did this. it might help.

There was air causing pipe banging in the loop, the house is one zone only. I closed the isolation valve on the return and purged the water out while introducing new water in through the pressure reducing valve. I kept it around 20psi while purging to push out all air in zone. Once the zone cleared up i set the boiler 12psi cold....all is well.

The reason why the boiler was short cycling was due to lack of pressure in the system. The gauge was not reading the correct psi. Switched that out as well so I had to drain the boiler...

I would have only had to drain the boiler once, but the supply house gave me a 1/4 NPT gauge and the 1/2 bushing they usually come with wasn't in the box....so I had to wait overnight and grabbed a bushing the next day...I just stuck a gauge on the boiler drain to keep an eye on it overnight....so yes I had to drain the boiler twice and it was short cycling when turned back on the first time because the gauge on the boiler was reading 12 psi when infact it wasn't.

Sounds like a goat show....and it was...unfortunately.

Tridicators often lie. As I get older I am convinced that the poor water quality in most residential boilers is the reason. We always carry our own pressure gauges when doing boiler service since the new condensing boilers will not operate below 10 psi.